1. Field of the Invention
The present invention relates to a reproducing apparatus for a disk-shaped recording medium comprising on the surface thereof spiral or concentric recording tracks to which information is recorded by moving a recording and reproducing head radially to the recording surface of the disk while rotating the disk-shaped recording medium. More specifically, the invention relates to a rotational velocity control method for a disk-shaped recording medium drive apparatus whereby the rotational velocity of the disk-shaped recording medium is quickly adjusted to changes in the position of the recording and reproducing head, as well as the medium, apparatus, and operating environment, to achieve optimum performance.
2. Description of the Prior Art
In general, disk-shaped recording media are recording using a constant linear velocity (CLV) method in which the linear velocity of the signal recorded to and reproduced from the disk remains constant as a means of increasing the recording density. This means that in order to maintain a constant linear velocity in all recording areas of the disk-shaped recording medium. the medium must be driven at a high rotational speed when reading data from the inside circumference part of the medium where the reproduction radius is smallest, and driven at a slower rotational speed when reproducing data from the outside circumference part of the medium where the radius is obviously greater. Therefore, as the position from which the signal is reproduced moves between the inside and outside circumferences of the disk, the recording and reproducing head must be moved radially t the disk while simultaneously adjusting the rotational speed of the disk according to the current position of the recording and reproducing head so that the head moves at a constant linear velocity relative to the disk medium.
The structure of a conventional reproducing apparatus RAc for a disk-shaped recording medium is shown in FIG. 29. Information is recorded to spiral or concentric recording tracks formed on the surface of the disk-shaped recording medium 1 using a magnetic, physical, optical, or other method, including combinations of these. The disk-shaped recording medium 1 is placed on a turntable 2 and held in placed from above by a clamper 3. The turntable 2 is connected to the spindle 5 of a spindle motor 4, and is thus driven rotationally by the spindle motor 4.
The pickup 6 is driven by a traverse motor 7 along slider 8 in the radial direction of the disk-shaped recording medium 1, thereby scanning the recording tracks of the disk-shaped recording medium 1 to generate the reproduced recording signal Spu.
The servo controller 9 is connected to the output of the pickup 6, and thereby amplifies the reproduced recording signal Spu after being applied with a servo control process to output the amplified reproduction signal SPU. The servo controller 9 also generates a traverse tracking error signal Sts, which is used to drive the tracking actuator built in to the pickup 6, based on the tracking information contained in the reproduced recording signal Spu. The servo controller 9 thus controls any change in the traverse movement of the pickup 6 between the recording tracks based on the traverse tracking error signal Sts.
Also connected to the servo controller 9, the clock extractor 10 extracts the clock component from the reproduction signal SPU read from the disk-shaped recording medium 1, and thus outputs the clock signal Sck. Based on the extracted clock component, the clock extractor 10 also generates the data reproduction clock signal Spl.
A decoder 17 is also connected to the servo controller 9 and clock extractor 10. Based on the data reproduction clock signal Spl supplied from the clock extractor 10, the decoder 17 applies various operations to the reproduction signal SPU to reproduce the data recorded to the disk-shaped recording medium 1. The reproduced data is output as reproduction data Sd. The decoder 17 also extracts the subcode data contained in the reproduction signal SPU to generate and output the subcode information signal Sq.
Based on the subcode information signal Sq supplied from the decoder 17 to which it is connected, the reproduction mode controller 20P generates the traverse movement signal Stm. The traverse movement signal Stm specifies the amount of traverse movement the pickup 6 is driven, i.e., how far the pickup 6 moves radially to the disk-shaped recording medium 1.
Connected to the servo controller 9 and reproduction mode controller 20P, the traverse motor driver 19 generates the traverse motor drive signal Stv based on the traverse tracking error signal Sts and the traverse movement signal Stm. The traverse motor 7 then drives the pickup 6 in the traverse direction based on the traverse motor drive signal Stv received from the traverse motor driver 19.
The reference clock generator 11 outputs a reference clock signal Sr1 of a known frequency. This predefined reference clock signal Sr1 is input with the clock signal Sck extracted from the reproduced recording signal Spu to the CLV error detector 12. The CLV error detector 12 compares the phase and frequency of the two clock signals Sr1 and Sck, obtains the frequency difference between the clock and thus outputs the CLV error signal Sc1.
The spindle motor driver 18 is connected to the output of the CLV error detector 12, and thus generates the spindle motor drive signal Sm for driving the spindle motor 4 based on the CLV error signal Sc1. The spindle motor 4 is thus driven based on the spindle motor drive signal Sm supplied from the spindle motor driver 18, and the disk-shaped recording medium 1 is thus rotationally driven in a specific manner.
The reproducing apparatus RAc further comprises a main controller 24 for controlling the overall operation of the reproducing apparatus RAc. The main controller 24 also comprises an input means whereby the user can operate the reproducing apparatus RAc.
The operation of the reproducing apparatus RAc thus comprised during CLV reproduction is described below.
When data is being reproduced by the pickup 6 from the inside circumference part of the disk-shaped recording medium 1 during CLV operation, the spindle motor 4 rotates at a faster speed than when data is reproduced from the outside circumference part of the disk in order to obtain the same, constant data rate. The speed of the spindle motor 4 is adjusted based on the CLV error signal Sc1 output from the CLV error detector 12.
What happens as the reading area of the disk-shaped recording medium 1 moves from the inside circumference toward the outside circumference of the disk is described below.
In this example it is assumed that a selection recorded at the inside circumference part of a music CD is being reproduced, and the user then operates the reproducing apparatus RAc to interrupt reproduction and immediately begin reproducing a selection recorded at the outside circumference of the disc. This reproduction area movement command (selection command) input by the user using the input means of the main controller 24 is then transferred from the main controller 24 to the reproducing apparatus RAc.
The main controller 24 calculates the track address of the recording area corresponding to the selection made by the user, and inputs the calculated target track address to the reproduction mode controller 20P. Based on the subcode information signal Sq, the reproduction mode controller 20P then compares the current track address with the target track address to generate the traverse movement signal Stm. The traverse movement signal Stm specifies how far in the traverse direction the pickup 6 must travel to reach the target track address, and is supplied to the traverse motor driver 19.
The traverse motor driver 19 thus drives the traverse motor 7 to move the pickup 6 along the slider 8 from the inside circumference side to the outside circumference side of the disk-shaped recording medium 1, and thereby position the pickup 6 to the appropriate recording track. Once the pickup 6 is positioned to the correct recording track, the reproduced recording signal Spu is read from the disk-shaped recording medium 1, the servo controller 9 amplifies the reproduced recording signal Spu, and the clock signal Sck is extracted by the clock extractor 10.
The disk-shaped recording medium 1 is still spinning at high speed after the pickup 6 moves from the inside to the outside circumference, however, and the clock frequency of the extracted clock signal Sck thus increases roughly proportionally to the radial movement of the pickup 6. The clock frequency of the clock signal Sck is thus significantly greater than the clock frequency of the reference clock signal Sr1. It follows that the value of the CLV error signal Sc1, which corresponds to the difference between the clock signals Sck and Sr1, is high.
The spindle motor driver 18 therefore causes the spindle motor 4 to decelerate so that the value of the CLV error signal Sc1 decreases, ultimately to zero. When the value of the CLV error signal Sc1 is zero, the clock frequency of the clock signal Sck is equal to the clock frequency of the reference clock signal Sr1. This means that the data read rate of the pickup 6 at the current radial position of the disk-shaped recording medium 1 is equal to the reference clock signal Sr1 output from the reference clock generator 11.
What happens as the reading area of the disk-shaped recording medium 1 moves from the outside circumference toward the inside circumference of the disk is described below.
As described above, the pickup 6 is moved from the outside circumference toward the inside circumference based on the destination recording track address (target track address) input from the main controller 24 to the reproduction mode controller 20P. This means that, just as when the pickup 6 moved from the inside circumference to the outside circumference, the optimum linear velocity required for reading from the new recording track at the inside circumference cannot be obtained because the disk-shaped recording medium 1 is still spinning at the rotational speed required to obtain the constant linear velocity necessary for reproduction from an outside circumference track. The clock frequency of the clock signal Sck extracted from the reproduced recording signal Spu read by the pickup 6 from an inside circumference track of the disk-shaped recording medium 1 is thus significantly lower than the clock frequency of the reference clock signal Sr1 generated by the reference clock generator 11.
If the value of the CLV error signal Sc1 is defined as a positive value when the pickup 6 traverses the disk from inside to outside circumference, the CLV error signal Sc1 value is negative after outside to inside circumference travel, but the absolute value of these positive and negative values are substantially the same for equivalent traverse movement. It is therefore necessary, in this case, for the spindle motor driver 18 to drive the spindle motor 4 to accelerate so that the value of the CLV error signal Sc1 is again zero and the linear velocity of the pickup 6 at the inside circumference track converges to the defined linear velocity of the disk-shaped recording medium 1 as obtained from the reference clock signal Sr1.
The data read rate is equivalent to the linear velocity of the pickup 6 relative to the recording track of the disk-shaped recording medium 1. CLV control is therefore used to maintain a constant data rate as the pickup 6 moves between the inside and outside circumference areas of the disk-shaped recording medium 1 irrespective of the current radial position of the pickup 6 on the disk-shaped recording medium 1. As a result, the clock extractor 10, reference clock generator 11, and CLV error detector 12 of the reproducing apparatus RAc described above can be thought of as a CLV controller 21 accomplishing the constant linear velocity drive control used by the reproducing apparatus RAc.
FIG. 30 is a graph of the relationship between the rotational speed of the disk-shaped recording medium 1 and the radial position of the pickup 6 on the disk-shaped recording medium 1 during CLV control. The radial position R is shown on the axis of abscissae, and the rotational speed N of the disk-shaped recording medium 1 is shown on the axis of ordinates. The values Rmin and Rmax indicate the radial positions at the first recording track on the inside circumference side and the last recording track on the outside circumference side of the disk-shaped recording medium 1.
Note that because information is recorded to this disk-shaped recording medium 1 at a constant linear velocity, the rotational speed N of the disk-shaped recording medium 1 changes in inverse proportion to the position R of the pickup 6 when reading data. The relationship between rotational speed N and position R can be expressed by the equation N.varies.1/2.pi.R.
With this type of reproducing apparatus for a disk-shaped recording medium, it is necessary to rapidly access and reproduce data from any specified part of the recording surface in response to user requests. The two major methods described below can be used to achieve this.
One is to move the pickup to a particular position after a read command from the user is received, wait for the rotational speed of the disk to stabilize after the pickup moves to the corresponding disk position, and then begin actual data reading from the target track. This method minimizes the access time. The other method is to maximize the target track scanning speed by the pickup, which determines the data read rate per unit time.
Access time in a conventional CLV-controlled reproducing apparatus for a disk-shaped recording medium is determined by the time required to increase or decrease the speed of the spindle motor 4 to achieve the constant linear velocity specified for the disk-shaped recording medium 1 when the pickup 6 moves from the inside to outside circumference or from the outside to inside circumference. In practice, it is therefore necessary to change the speed of the rotational drive train comprising the rotating disk-shaped recording medium 1, turntable 2, clamper 3, spindle motor 4, and other components suddenly and stably, using a braking force proportional to the rotating mass and the square of the rotational speed.
Because this rotational drive train is also spinning at high speed, the change in the rotational speed according to the access position also increases when the rotational speed of the media increases. For example, a CD-ROM operating in the 1.times. mode spins at approximately 500 rpm when reproducing data from an inside circumference track, and at approximately 200 rpm when reproducing data from an outside circumference track. The difference is approximately 300 rpm or approximately 2.5 times between inside and outside circumference tracks. However, when a CD-ROM is driven in the 4.times. mode, the disc spins at approximately 2000 rpm at the inside circumference track, and at approximately 800 rpm at the outside circumference track, a difference of approximately 1200 rpm.
As this speed difference increases, the spindle motor torque required to adjust the disk speed in a given unit of time increases. This means that if the spindle motor torque is low, the access time, i.e., the time required for the rotational speed of the disk to stabilize at the required constant linear velocity, increases. High torque spindle motors are therefore required to maximize access time as the spindle speed increases. This leads to unavoidable increases in power consumption and cost as the motor size contributing to the reproducing apparatus it self increases to provide the necessary torque.
The scanning speed of the pickup also cannot be simply determined because the data read rate changes in proportion to the scanning speed of the pickup. Specifically, the maximum scanning speed must be set so that the data read rate is less than the maximum processing speed of the signal processing circuitry of the reproducing apparatus, or the maximum rotational speed of the rotational drive train. In practice, however, the maximum scanning speed must be set to a lower rate in order to provide a tolerance range to compensate for variations in the quality of the disk-shaped recording medium, the rotational drive train components, and the signal processing circuitry, changes in operating characteristics over time due to heat from operation, and even simple deterioration from extended use. If this tolerance range is insufficient, the drive apparatus for the disk-shaped recording medium may malfunction during operation. If the tolerance range is too great, the specified characteristics and performance of the disk-shaped recording medium will be wasted.
Therefore, the object of the present invention is to provide a drive apparatus for a disk-shaped recording medium whereby any desired part of the recording surface of the disk-shaped recording medium can be rapidly accessed, data can be read at high speed, and optimum performance can be achieved according to the condition of the medium, apparatus, and operating environment.